1. Technical Field of the Invention
This invention relates to a vehicle power supply system, and is applicable to the prevention of a vehicle fire which is caused by the power supply damage which may occur at the time of vehicle collision.
2. Description of the Related Art
Recently, a variety of electronic devices (hereinafter referred to as "loads", when applicable) have been mounted on vehicles. Power supply lines, control lines, and output lines to those loads are bundled into a wire harness or harnesses so that power is supplied to the loads and the loads are connected to one another.
Electric power is supplied to the load from the battery. In this connection, in order to prevent the occurrence of troubles in the power supply system, a kind of fuse, namely, a fusible link is provided which is longer in fusing time than an ordinary fuse. Through the fusible links, power is supplied to the load from the battery.
If the cover of the power line connected to such a load, is removed and grounded, then large current flows from the battery, so that the part of the power line (wire) thus grounded is heated greatly to set out a fire; however, a large current flows in this manner, the fusible link is fused to interrupt the flow of current from the battery, thereby to prevent the occurrence of a fire, to secure the vehicle.
As was described above, a trouble occurs with the power supply system in a conventional vehicle, the fusible link connected to the battery is fused with the large current occurred by the trouble to secure the vehicle.
On the other hand, in the case where the load is located away from the battery, and its operating current is small, the power supply line is relatively thin, and accordingly high in resistance. Hence, even if the cover of the power supply line is removed and grounded; that is, even if over-current flows through the power supply line, the fusible link is not fused. Accordingly, it is impossible to prevent the occurrence of a fire which is due to the over-heating of the power supply line.
In order to overcome the above-described difficulty, a power supply interrupting system has been proposed in Unexamined Japanese Patent Publication Hei 6-321027. The system is as shown in FIG. 3. That is, a current detecting section 4 to detect the amount of a current flowing through a fusible link 2 is provided on a power supply line 3, and a total current calculating section 8 is provided which calculates the value of current used by an electronic device (load) which receives electric power through the power supply line 3. Furthermore, a control section 9 compares the value of current detected by the current detecting section 4 with the total current value calculated by the total current calculating section 8, thereby to determine whether or not a power trouble occurs. In the case it is determined where the power trouble has occurred, a control voltage is applied to a silicon controlled rectifier (SCR) 5.
When the control voltage is applied to the control terminal of the SCR 5, the SCR 5 is rendered conductive, so that a large current flows through the fusible link 2 and the SCR 5 from the battery 1. As a result, the fusible link 2 is fused, so that the supplying of electric power to the loads on the vehicle is interrupted; that is, the vehicle is secured.
In FIG. 3, a vehicle monitoring control system 6 detects and monitors the operating conditions of the various devices, whether or not electric power is supplied to them, through a state monitoring section 7. The data thus are supplied to the total current calculating section 8. The values of currents used for the various devices (when electric power is applied to the devices) are previously stored in the total current calculating section 8. The total current calculating section 8 calculates the total current value of the devices in which the power is supplied, which is input by the state monitoring section 7, with reference to the stored current values and applies the total current value to the control section 9.
Namely, the power interrupting system shown in FIG. 3 is designed as follows: That is, when a trouble occurs with the power supply system, the current detecting section 4 detects an abnormal current pulse, and the control section determines it as an abnormal pulse and applies the result of determination to the SCR 5, so that fusible link 2 is fused.
However, in the above-described fire preventing system, the over-current which attributes to the dead short or rare short of the power line is determined from a delicate pulse difference. This determination is considerably difficult, and suffers from a problem which makes it difficult to positively prevent a vehicle fire.
Further, the current detecting section 4 shown in FIG. 3 is expensive. Hence it is rather difficult to employ it in the power source system.